1. Field of the Invention
The present invention relates generally to an apparatus for atomizing a liquid product which can be integrated into aerosol packs, which may be pre-pressurized. Such an apparatus may be integrated into a spray can, which is operable by simply pushing a closure mechanism to open valves for dispensing the contents of the can.
2. Background of the Invention
A conventional apparatus for atomizing a liquid product containing the actual active ingredient uses pressure from a propellant, which is contained within a conventional storage container connected thereto or alternatively a pump to pressurize the storage container. Such known devices use a tube to transport the liquid product to be atomized to an atomizing nozzle where droplets are formed from the liquid product. In order to effectively atomize a liquid product by a conventional atomizing apparatus, comparatively large volumes of propellant, diluents and/or solvent, in relation to the liquid product are necessary, both for providing sufficient pressure for the atomization process and for reducing the viscosity of the liquid product, that has the actual active ingredient of the system. The propellant is conventionally used in a volumetric ratio of 2000:1 to 20,000:1 of gas to liquid product, when determined at atmospheric pressure. The propellant may be compressed air, nitrogen, or, conventionally a volatile organic compound such as butane and chlorinated or fluorinated hydrocarbons, which are liquid in a compressed state.
In conventional systems, the liquid product has to be diluted further by additional solvents, or diluents (such as, for example, liquefied natural gas), which also act as the propellant and reduce the amount of active ingredient atomized at the conventional high flow rates and/or reduces the viscosity of the active ingredient. The propellant itself may act as a solvent and/or diluents for the liquid product when contained within the same compartment as the liquid product, (such as, for example, when the propellant is liquefied natural gas, butane, chlorinated hydrocarbons, or fluorinated hydrocarbons). When both liquid product and propellant are contained within the same storage container, such as in the conventional “dip tube” systems, some of the propellant may disperse or dissolve into the liquid product. In order to reduce such high total flow rates of known dip-tube systems, they conventionally need a so-called vapor tap to allow inflow of additional propellant in its gaseous state, which reduces the flow rate of liquid mixture up the dip-tube. This reduction of the flow rate by additional gaseous propellant is used in conventional systems to reduce the amount of liquid product which is dispensed while maintaining a sufficiently high total flow rate which is necessary for a stable atomization.
In conventional systems, when liquid product is being dispensed, the effect of the propellant to act as a solvent or diluent for the liquid product is significantly reduced as the propellant changes into its gaseous phase, and becomes no longer available as a liquid solvent.
An apparatus for atomizing liquid product is disclosed in U.S. Pat. No. 5,921,439, which uses a nozzle to atomize a mixture of pressuring gas and liquid product. The liquid product and pressurizing gas form a mixture immediately before entering the atomizing nozzle, but are delivered to the mixing compartment by separate tubes. In the storage compartments, the pressurizing gas exerts its pressure also on the liquid product, which is isolated from the pressurizing gas within a collapsible bag, surrounded by pressurizing gas.
U.S. Pat. No. 5,918,817 discloses a two-fluid cleaning jet nozzle, which has an atomizing unit by which pressurized gas can atomize a liquid into droplets. The cleaning jet nozzle in U.S. Pat. No. 5,918,817 consists of two portions, namely a so-called atomizing tube and a cross-sectional area of 7–200 mm2 into which the liquid and gas are introduced. This atomizing tube is provided with one exit port, which continues into an accelerating tube having a smaller diameter than the atomizing tube, namely 3–15 mm2. As a result of the smaller cross-sectional area of the accelerating tube being fed from the atomizing tube which has a larger cross-sectional area, the velocity of the exiting fluid droplets is much higher than for conventional nozzles without a smaller diameter accelerating tube adjacent to the atomizing tube. This two-compartment jet nozzle provides almost double the exit velocity of atomized fluids at the same pressure of the propellant gas in comparison to the conventional jet nozzle, i.e., approaching the speed of sound at a supply pressure of gas about 3 bar. It becomes clear from the drawing, that the entrance port for the gas is always of a bigger cross section than the entrance port for liquid. U.S. Pat. No. 5,918,817 emphasizes the importance of a high velocity and a high volume to be obtained for the stream of liquid droplets in order to effectively remove contamination from the surface of silicon wafers.
Conventional aerosol spray systems typically produce flow rates of 0.5 to 3 grams-per-second (g/s) of product, where the product is a mixture of liquefied propellant gas, a diluent or solvent and a small amount of active ingredient. In these systems, both the propellant gas and the diluent or solvent are often volatile organic compounds, such as butane and ethanol. These volatile organic compounds are included to produce a spray with a “cool feel” as they quickly evaporate leaving behind just the active ingredient on the sprayed surface (such as, for example the skin) or suspended in the air. Conventionally, a mixture of organic compounds is needed for adjusting the viscosity and solvency of the active ingredient (i.e., a liquid product without added volatile organic compounds). The volumetric ratio of gas (at atmospheric pressure) to active liquid product is typically between 2000:1 and 20,000:1. The propellant gas, the solvents and diluents are released into the atmosphere, which generates environmental problems.
It has been shown that conventional valve arrangements for atomizing apparatuses necessitate the use of flow rates of propellant and liquid product including any diluents in the order of 0.5 grams per second to 1.5 grams per second in order to avoid unstable (i.e., oscillating) flow. With lower total flow rates, the flow at the exit port becomes unstable and discontinuous, i.e., it oscillates. In order to reduce such high flow rates of propellant, dip-tube systems conventionally need a so-called vapor tap to allow inflow of additional propellant in its gaseous state.
The design of conventional atomizing valves usually has an internal cavity volume arranged between afferent pathways for delivering liquid product and/or propellant and the exit. For example, the atomizing nozzle is at least 100 mm3 and the total cavity volume, including valve body, stem and actuator, is between 100 and 300 mm3.